c runtime error message

this error appeared while creating file using fo开发者_运维问答pen in c programming language

the NTVDM cpu has encountered an illegal instruction CS:0000 IP0075 OP:f0 00 f0 37 05 choos 'close to terminate the operation

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This kind of thing typically happens when a program tries to execute data as code. In turn, this typically happens when something tramples the stack and overwrites a return address.

In this case, I would guess that "IP0075" is the instruction pointer, and that the illegal instructions executed were at address 0x0075. My bet is that this address is NOT mapped to the apps executable code.

UPDATE on the possible connection with 'fopen': The OP states that deleting the fopen code makes the problem go away. Unfortunately, this does not prove that the fopen code is the cause of the problem. For example:

• The deleted code may include extra local variables, which may mean that the stack trampling is hitting the return address in one case ... and in the other case, some word that is not going to be used.

• The deleted code may cause the size of the code segment to change, causing some significant address to point somewhere else.

The problem is almost certainly that your application has done something that has "undefined behavior" per the C standard. Anything can happen, and the chances are that it won't make any sense.

Debugging this kind of problem can be really hard. You should probably start by running "lint" or the equivalent over your code and fixing all of the warnings. Next, you should probably use a good debugger and single step the application to try to find where it is jumping to the bad code/address. Then work back to figure out what caused it to happen.

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Assuming that it's really the fopen() call that causes problems (it's hard to say without your source code), have you checked that the 2 character pointers that you pass to the function are actually pointers to a correctly allocated memory? Maybe they are not properly initialized?

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Hmmm.... you did mention NTVDM which sounds like an old 16 bit application that crashed inside an old command window with application compatibility set, somehow. As no code was posted, it could be possible to gauge a guess that its something to do with files (but fopen - how do you know that without showing a hint?) Perhaps there was a particular file that is longer than the conventional 8.3 DOS filename convention and it borked when attempting to read it or that the 16 bit application is running inside a folder that has again, name longer than 8.3?

Hope this helps, Best regards, Tom.